What do 5.56mm & 7.62mm mean?

When looking at suppressors, you’ll notice that most rifle suppressors are categorized using the bore diameter, in millimeters, instead of a specific caliber.  Those metric measurements can be confusing at first since people are often looking for a suppressor for a specific weapon – and generally have the caliber in mind instead of the bore size.

On top of that, for many of us it isn’t very common to think in metric terms – which can complicate the issue since we have to figure out what diameter we really need.

Regardless, this isn’t very hard once you realize that there are only a few bullet diameters that are in wide-scale use – and the point of this article is to help you match the correct suppressor to your weapon.

7.62mm Rifle Suppressors

The first family of calibers is the ever-present .30.  In this family, you’ll find calibers like .308, .30-30, .30-06, .300WM, and many more.  Calibers designations are, for the most part, named in inches – so all of these calibers use a .308″ diameter bullet (although each has different pressures & optimal bullet weights).

Even though these calibers use a .308″ diameter bullet, the lands in the rifling measure .3″ – which is where the .30 designation comes from.  Now, if you pull out your handy-dandy unit conversion calculator, you’ll see that .3″ converts to exactly 7.62mm.  That’s easy enough!

What this means is that if you have a .30 caliber weapon (or smaller), you can put a 7.62mm suppressor on it and the bullet will fit through without striking the baffles.

Of course, you also need to be sure the suppressor you pick will handle the pressure of your caliber.  The general rule is that any of the 7.62mm suppressors will handle pressures up to .308.  The next level of suppressors will generally handle pressures up to .300 WM; and, for anything higher than that, you should often just jump up to the .338 LM suppressors.

5.56mm Rifle Suppressors

The second major category of rifle suppressors is designed around the .223″ &.224″ diameter bullets.  These can include calibers like .223, 5.56mm & .22-250.

If you plug .223″ into the conversion calculator you’ll actually come up with 5.6642 mm; but, as with the 7.62mm calibers, the 5.56mm measurement actually comes from the lands in the rifling – which measure 5.56mm.

Once again, you’ll need to watch the pressure of your caliber if you decide to go with anything higher pressure than 5.56×45 NATO – which is the caliber used by many AR15, M4, and M16 weapons.

Suppressors for Intermediate Rifle Calibers

There are some calibers, like .243 & 6.8 SPC that fit in the gap between 5.56mm & 7.62mm suppressors.  For these calibers, you are typically going to need to go to the next step up for your suppressor.  In most cases, that next step up will be 7.62mm; but, there are some 6.8mm suppressors available on the market if you want to match the suppressor bore a bit more closely to your bullet size.

Why do you want to match the bore size to the bullet size?  The reason is that the suppressor will be more efficient; or, in other words, a smaller suppressor can be quieter than a larger suppressor if the suppressor bore of the smaller suppressor matches the bullet size more closely; but, that’s a topic for another day.

Conclusion

Overall, this is actually pretty simple, and can be summed up with just a few points:

• Any of the .30 caliber weapons will use a 7.62mm suppressor
• Any of the .223/5.56mm weapons will use a 5.56mm suppressor
• You can put a smaller caliber bullet through a larger bore suppressor – but it won’t be as efficient as as a suppressor where the bore size is matched more closely